LABORATORY FOR ELECTROMAGNETIC AND ELECTRONIC SYSTEMS

The mission of the Laboratory for Electromagnetic and Electronic Systems
(LEES) is the focus for research and teaching in electric energy from its
production through its processing to its utilization, and in electromechanics
from the macroscopic through the microscopic to the molecular levels. Electric
energy and electromechanics are defined broadly to include power systems
monitoring and operation; automatic control; power electronics; high voltage
engineering; and conventional, continuum and biological electromechanics. Much
of the work of the laboratory is experimental, and industrial sponsorship
represents a large fraction of the laboratory's support. The laboratory's
professional staff consists of 10 faculty from EECS, one Senior Lecturer, 2
Senior Research Engineers, 6 research staff, and approximately 50 graduate
students. The laboratory faculty and most of the staff are heavily involved in
both undergraduate and graduate teaching. Faculty from the departments of ME,
CE, MS&E and NE are collaborators in many of the laboratory's programs, and
there are extensive joint activities with the Microsystems Technology
Laboratory (MTL) and the Energy Laboratory. LEES is also an active participant
in the Leaders for Manufacturing Program, and the Technology and Policy Program
(TPP). During the past year the laboratory has experienced a continued
expansion of its automotive related research, demonstrated a 1/5 scale Maglev
test facility for high temperature superconductors, and created a consortium on
Transmission Provision and Pricing Under Open Access.

AUTOMOTIVE ELECTRONICS AND ELECTRICAL SYSTEMS

Professor John G. Kassakian and Dr. Thomas M. Jahns lead the
laboratory's work in automotive electrical and electronic systems. This work is
sponsored primarily through the laboratory's Consortium on Advanced Automotive
Electrical and Electronic Components and Systems. Four new members were added
to the consortium in the past year, bringing the membership to 13. The
consortium held four two-day meetings and organized a major industry wide
workshop to promote the adoption of 42 volts as a standard for future
automotive electrical systems. The laboratory has also engaged in a strategic
alliance with Ford to accelerate the adoption of this standard. Under the
auspices of the consortium, the multi-attribute trade-off analysis tool MAESTrO
has been upgraded to near commercial quality by an outside software developer.
Professors James L. Kirtley and Jeffrey H. Lang, Dr. Jahns and graduate student
Edward Lovelace have been investigating the designs of high power
starter/alternators for future cars. Permanent magnet, induction, switched
reluctance, hybrid induction and Lundell machines have been considered. A
prototype of the most promising design will be built and tested during the next
year.

Under sponsorship from Daimler-Benz, Dr. Jahns and graduate students Khurram
Afridi and Isaac Trefz have adapted MAESTrO for application to the electrical
systems of trucks and buses. This work has been very favorably received by
Daimler-Benz.

With graduate student Deron Jackson, Professor Steven B. Leeb has continued
development of a 3 kW prototype of a battery charging system for electric
vehicles employing a non-ohmic, magnetically-coupled connector system. A
bi-directional version of the charger has been completed that permits both
carefully controlled battery charging from the utility, and also controlled
discharging of the battery back into the utility. This bi-directional
capability is essential for ensuring maximum battery life. Other applications
for non-ohmic power transfer are under investigation, including incorporation
into marine refrigeration units and hinged, fire-resistant power couplings for
doors.

Mr. Thompson completed his Ph.D. thesis with the design, test and analysis of a
1/5 scale magnetically levitated (Maglev) train test facility suitable for
high-temperature superconductors. A new low cost multiple loop guideway was
built and tested, and resultant electrodynamic forces were measured at actual
Maglev train operating speeds. The results were compared to predictions based
on simple circuit models, with close correlation. The test fixture was also
used to validate the concept of lift generation at zero velocity by ac
excitation of the main magnet coils. In further tests, a novel magnetic active
secondary suspension was tested. Results show that it may be possible to
actively control ride quality by varying the high temperature superconducting
coil currents, removing the requirement for a mechanical suspension for ride
control.

Mr. Perreault completed his Ph.D. thesis on position sensing and communication
between guided vehicles operating under automatic control. The system allows
vehicles to keep accurate track of the position of other vehicles and to
communicate messages between vehicles and from a vehicle to a central control.
The system does not make use of radio waves and is suitable for use with almost
any type of guidance and propulsion system.

Mr. Macgreggor completed his M.Eng. thesis on fault tolerant control for
automated transportation. He demonstrated a multiprocessor system that can
sense when any one processor fails and take corrective action to eliminate any
accident that might occur without fault tolerant protection.

MODELING, MONITORING AND CONTROL OF POWER SYSTEMS

Utility industry restructuring has placed an intense focus on achieving
economically optimal system operation by employing new and more sophisticated
control and monitoring strategies. LEES has been making significant
contributions to the solutions of problems of power system modeling, economic
control, and apparatus monitoring.

Modeling and Control
Professor Bernard Lesieutre and graduate student James Hockenberry have
developed a nonlinear thermostatic load model as part of Professor Lesieutre's
ongoing research on power system dynamic load modeling sponsored by the NSF. In
previous work the importance of proper load models has been demonstrated, an
improved probabilistic aggregate model of a cluster of induction motors was
developed, and common lighting and power electronic loads were investigated.
The new thermostatic load model captures important characteristics that are
lacking in traditional "voltage recovery" and linear system models. Professor
Lesieutre has also begun new research in the area of uncertainty analysis in
large scale power system simulations.

A great deal of power system practice is dependent on transient simulators, but
these are often used uncritically and without insight. Professors Lesieutre and
George C. Verghese have initiated work on intelligent simulation aids for power
system transient simulators. They are also continuing their studies of new
approaches to reduction of large power system dynamic models, with a view to
reducing simulation times.

Professor Verghese and graduate student Ben Leong, in collaboration with Dr.
Joseph Thottuvelil of Lucent Technologies, have been conducting pioneering
studies of the interesting dynamic properties of broadband power networks that
are being put into place to power coax/optical fiber communication networks.
The loads on these networks are regulated power electronic supplies, which are
activated once the voltage across their input exceeds some threshold. The
results obtained thus far describe the dynamic and steady-state properties of
these nonlinear networks, provide guidance on what choice of threshold voltage
will ensure that the network settles into a desirable steady state, and also
suggest simple approximate calculations that provide rapid yet accurate
numerical results.

Dr. Marija Ilic, in collaboration with Professor Francisco Galiana of McGill
University and the Energy Laboratory's Electric Utility Program, has created
the Consortium on Transmission Provision and Pricing Under Open Access. The
consortium is studying issues related to the operational stability of the
regional power grid in the face of the relaxed control over individual
generators implied by the deregulation of the electric utility industry.

Professor Lesieutre, Dr. Ilic and Professor Verghese were the organizers and
hosts of the North American Power Symposium held at MIT in October 1996. The
Symposium included a session on challenges under deregulation and a plenary
talk on the major summer blackouts of 1995. It drew world-wide participation
and was highly successful.

Adaptive Monitoring of TransformersResearch Engineer Wayne Hagman and graduate students Mary Jane Boyd and
Paul Barrett have completed the design for the next generation of software for
the MIT Adaptive Transformer Monitoring System, including enhanced intra-system
inter-process communication of data information. Mr. Hagman has also trained a
number of Boston Edison employees in the use and maintenance of the MIT systems
that are monitoring five of Boston Edison's large substation transformers. Ms
Boyd has also developed artificial intelligence methods for the integration of
spatial and temporal information in the detection of anomalies, and knowledge
elicitation and structuring in the context of on-line power apparatus
monitoring.

Principal Research Engineer Chathan Cooke has demonstrated, on an energized 500
kV power transformer at Consolidated Edison, a system capable of on-line
detection of defects that induce internal partial discharges (PDs) in large
power transformers. The system uses advanced time and frequency domain signal
processing to identify and locate PD events. A tear-down of the transformer
showed excellent correlation between the measured PD signals and actual
tracking damage of the internal winding. Dr. Cooke is now making the
measurement system robust enough for field application.

Professor Lesieutre and graduate student Reza Olfati-Saber have developed a
neural state space model (NSSM) for describing the relations between
temperature and measured dissolved gas content in transformer oil. The
advantage of the NSSM approach is that the unknown functional form for the
components of a traditional nonlinear state space model can be approximated by
neural networks and estimated from measured data. The NSSM model should
significantly improve the transformer thermal model and facilitate the
detection and diagnosis of certain problems, and allow better evaluation of the
present condition for purposes of dynamic loading.

The laboratory's efforts to team with an appropriate company to produce and
market a transformer monitoring system based on the technology developed in
LEES appears to have been successful. It is expected that by August, 1997, an
agreement will be in place that both licenses the technology and provides
funding for continued research.

Non-Intrusive Load MonitoringProfessor Leeb, in collaboration with Professor Leslie K. Norford of the
Department of Architecture, and with graduate student Steven R. Shaw, have
demonstrated techniques that extend the capabilities of the Nonintrusive Load
Monitor (NILM) to the determination of power quality, i.e., current waveform
shape, anywhere in a monitored building. Also, diagnostic techniques have been
developed that permit the NILM to determine the parameters of models describing
important loads, e.g., induction motors, solely from partial electrical
measurements made at the utility service entrance. A second patent on the NILM
technology will be awarded in 1997. A field portable platform capable of
implementing not only the NILM algorithm but also the power quality and
diagnostic techniques will be completed this year and tested in on-campus
buildings and off-campus manufacturing operations.

ELECTROMECHANICSElectrical Machines
The Novice Design Assistant (NDA), a computer aided tool for designing
three-phase induction motors developed by Professor Kirtley and graduate
student Ujjwal Sinha, has been enhanced by the development of a technique based
on multi-dimensional adaptive regressive splines for adapting the design space
for use with an NDA design synthesis. Work is progressing to build the NDA into
the production design software of Magnetek, the sponsor of this research.

Gel Polymer Actuators
Professor Leeb, in collaboration with Professor Toyoichi Tanaka of the Center
for Materials Science and Engineering, and with graduate students Ahmed
Mitwalli, Deron Jackson and Tim Dennison, continue to explore applications of
polymer gels as actuators and sensors. Building on last year's demonstration of
a thermo-optical gel sensor for metal ion detection, a new multi-sensor
apparatus has been constructed that estimates, in real time, the transition
temperature at a number of positions in a long gel. This sensor is being used
to explore the possibility of identifying the components of a mixture by using
the gel as a chromatogram. For example, if the constituents of a given mixture
exhibit different mobilities in the gel, the gel could serve as a
chromatographic or electrophoretic medium for separating the mix. As the mix
separates, different regions of the gel exhibit different phase transition
temperatures, which correspond to the local concentrations of the constituents.
Optical sensors, placed along the length of the gel to scan the different phase
transition temperatures in different regions of the gel, could be used to
identify the components of the mix.

Work is also underway to develop new imaging techniques for "soft" materials
like gels. Professor Leeb and Mr. Dennison are working to use the Faraday
effect to develop tomographic imaging techniques for optically translucent
materials with differing Verdet constants. These new imaging technologies might
ultimately be used to develop more sophisticated approaches for examining
spatial separation in phase transition chromatography experiments.

Biological Electromechanics
Professor Martha Gray and her group have made important strides in their work
on the use of magnetic resonance (MR) methods for measuring the composition and
functional integrity of cartilage. Specifically, they have demonstrated that a
method designed to measure the fixed charge density of cartilage corresponds
quantitatively to destructive biochemical measures of charge and qualitatively
to histological measures. Moreover, they have established that their methods
are feasible in a clinical setting with pilot studies revealing information not
available with traditional MRI scans. This method offers the potential to
monitor cartilage disease progression and therapeutic efficacy with a
specificity and sensitivity not previously available.

POWER ELECTRONICS

Professor Kassakian, with graduate students David Perreault and Kenji Sato,
have completed the construction and testing of a prototype 6 kW unity power
factor rectifier designed using the cellular architecture that they have been
studying for several years. A new single-wire, but robust, current sharing and
interleaving scheme has also been incorporated in the prototype. This highly
reliable, and potentially very economical, power electronic architecture is
currently being applied to advanced automotive applications where the cost and
reliability of power electronics has been a major obstacle to its penetration
of the automotive market.

Professor Verghese, with Dr. Joseph Thottuvelil of Lucent Technologies and
David Perreault have developed and tested the first precise criteria for
stability of paralleled power converters under active current sharing. These
results are already being applied by designers at Lucent and elsewhere.

Professor Verghese in collaboration with Professor Aleksandar Stankovic of
Northeastern University, Professor Paolo Mattavelli of the University of
Padova, Italy, and graduate students Vahe Caliskan and Chalee Asavathiratham,
have continued - with support from the NSF - to demonstrate the efficacy of
harmonic averaging methods in constructing frequency-selective dynamic models
for power electronic components. These models permit the user to focus on the
behavior of interest, while suppressing irrelevant detail. they are well
matched to the phasor representations used in power system applications, lead
to much faster simulations and more tractable starting points for control
design, and are more accurate than those obtained by traditional averaging
methods.

Professor Anantha Chandrakasan with graduate students Rajeevan Amirtharajah,
Abram Dancy and Vadim Gutnik have developed embedded power techniques for
portable electronic systems. They have shown that providing a feedback path
from the digital signal processor to the power supply module can reduce the
power dissipation of the processor. Rather than designing a feedback system
around the power converter to fix the output voltage, it is better to allow the
voltage to vary such that the timing constraints are just met at any given
temperature and operating conditions. They have also developed a variety of
techniques for achieving high efficiency at low voltages and power levels which
include delay line based pulse width modulation, low resolution feedback,
voltage quantization, etc. Mr. Amirtharajah extended this work to develop a
self-power system where the energy required by the electronics is derived from
the environment (e.g., motion). Such techniques will be critical for future
battery operated wireless sensors. This work was recently reported in a Nikkie
Times article in Japan.

HIGH VOLTAGE AND INSULATION RESEARCH

Professor Lesieutre and Professor Markus Zahn, with graduate students
Alexander Mamishev and Yanqing Du, have redesigned the MIT-developed
three-wavelength dielectrometry sensor to maximize its signal to noise ratio
and to minimize cross-coupling effects between wavelengths. They have also
conducted experiments to study the diffusion process of moisture between oil
and pressboard to better understand and quantify the flow electrification
problem in transformers, which can lead to a transformer failure when a cold
transformer is energized.

Professor Zahn and graduate student Afsin Üstündag have
extended their mathematical formulation that allows reconstruction of an
applied electric field from light intensity measurements using electric field
induced birefringence (Kerr effect) even when the magnitude and direction of
the electric field varies along the light path. Using an "onion-peeling" method
it is possible to calculate from light intensity measurements the magnitude and
direction of an applied electric field. This methodology is being used to
research the effects of charge injection on electrical conduction and breakdown
behavior in high field stressed dielectrics. Graduate student Tza-Jing Gung has
performed numerous confirming experiments using needle-to-plane electrodes
stressed by high voltages.

Dr. Cooke and graduate student Robert Lyons have enhanced their ultrasound
method for detecting charges and defects within XLPE polymer power cables. They
have increased the resolution of the measurement system and applied it to the
detection of localized space-charge phenomena at high applied stresses, and
have observed distinct charge processes just prior to the electrical treeing
breakdown failure. An improved system to observe charge conditions prior to
tree inception is under construction. This will allow direct observation of the
details of the micro-processes and to compare the results with theory.

In cooperation with Tokyo Electric Power Company's research laboratory (TEPCO),
Dr. Cooke has established an internet link to exchange data from ultrasound
charge measurement experiments at TEPCO and MIT. This link allows daily
cooperative communication, including audio, video, and file sharing between
groups, and direct viewing of the remote experiments. The link is used to
compare experimental results and models for charge transport in XLPE polymer
power cables.

PERSONNEL CHANGES

Mr. Paul Warren, a longtime Research Engineer in LEES left the laboratory to
join the research activities of the Gas Turbine Laboratory. Mrs. Barbara
Connolly and Mrs. Kathleen McCue both retired from MIT during the last year.

Dr. Thomas M. Jahns, on a two year sabbatical leave from General Electric's
Corporate Research and Development Laboratory, has joined LEES as Senior
Lecturer and is working closely with Professor Kassakian. Ms Karin
Janson-Strasswimmer and Ms Sara Wolfson have joined the laboratory as Senior
Secretaries.